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7 décembre 2017: 1 événement

séminaire

Séminaire LCB

Jeudi 7 décembre 2017 14:00-15:00 -
Xinxin Qian (Equipe Wu)

Séminaire LCB

Résumé : High diversity of ellipsoidal multicellular magnetotactic prokaryotes in the Mediterranean Sea and analysis of their structure and magnetosome compositionMagnetotactic bacteria (MTB) are unique in their ability to synthesize intracellular membrane-bounded minerals of magnetite (Fe3O4) or greigite (Fe3S4). MTB display various morphologies, the most remarkable forms are multicellular magnetotactic prokaryotes (MMPs). MMPs are highly motile aggregates composed of 10–60 phylogenetically identical gram negative cells. Two morphotypes of MMPs have been identified : spherical MMPs (sMMPs) and ellipsoidal MMPs (eMMPs). MMPs are fascinating model organisms in the study of the origin, evolution and development of prokaryotic multicellularity as well as bacterial magnetic biomineralization.eMMPs have been collected from intertidal sediments of the Yellow Sea in Qingdao and Rongcheng, the Mediterranean sea at Saintes-Maries-de-la-Mer, Port-Saint-Louis-du-Rhône, Fos-Sur-Mer, Port de Bouc, Carry-le-Rouet, L’Estaque, Point-Rouge, Calanque de Sormiou, Calanque de Morgiou, Saint-Cyr-Sur-Mer, Bandol, Sanary-sur-Mer, Six-Fours-les-Plages, Mandelieu-la-Napoule and Antibes. Compared to spherical MMPs much less, about 5, species of ellipsoidal MMPs had been identified worldwide when I started my thesis. Our previous analysis has identified an eMMPs isolated from Six-Fours-les-Plages that shares 100% sequence identity of the 16S rRNA gene with the e-MMP isolated from Rongcheng China. Therefore, I choose Six-Fours-les-Plages as a sampling site to study the diversity, assembly, structure and genomes of of eMMPs. Using magnet-collection and race-track purification followed by 16S rRNA gene amplification and sequencing I have identified 4 new species and one new genus of MMPs. I optimized the correlative fluorescence-scanning electron microscope technique (FISH-SEM) and confirmed their taxonomies authenticity, and revealed the variation in magnetosome numbers and chain alignment depending on the species analyzed. STEM-EDX mapping analysis indicates bullet-shaped magnetite magnetosomes in e-MMPs. In collaboration with Chinese colleagues using micro-manipulation sorting and sequencing we have extended the total diversity of the Mediterranean eMMPs to about 2 dozen species and more than 5 genera. Four genomes have been partially sequenced. These results show a great diversity of the ellipsoidal MMPs. I’ll also present electron microscope results about the assembly and architecture of the Mediterranean MMPs.